Improving the fuel efficiency of diesel engines, used in machinery of all types, can result in substantial saving in fuel costs for the operator. Known fuel efficiency tests conducted in the field relate fuel consumption and emissions to Units of Time or Distance (i.e. gallon/hour or miles/gallon), rather than gallons/horsepower or gallons/kilowatt hour. However, tests conducted that are based on actual delivered horsepower eliminate many of the variables, that when unaccounted for, negatively impact the accuracy of results. For example, in determining the fuel efficiency of a diesel engine in a towboat, the variables might be wind, water current, etc.